Foldable and portable ocular systems

ABSTRACT

There is a need for robust and portable system, and apparatus for ophthalmology. We propose use of foldable ophthalmic system. Our system will have a chin-rest (or face-rest or forehead rest) that can be folded so that the ocular device could be transported in a brief-case type casing. Our system can be used for many modalities including optical coherence tomography.

CROSS REFERENCE TO RELATED APPLICATIONS

The instant application is a continuation application and claimspriority to the pending U.S. patent application Ser. No. 15/624,689titled “Foldable Ophthalmic System” filed on Jun. 15, 2017. The entiredisclosure of the U.S. patent application Ser. No. 15/624,689 is herebyincorporated by this reference in its entirety for all of its teachings.The application Ser. No. 15/624,689 is a continuation-in-partapplication and claims priority to the U.S. patent application Ser. No.14/757,749 (now patented with U.S. Pat. No. 9,717,406) titled “CompactFoldable Apparatus for Ophthalmology” filed on Dec. 22, 2015. The entiredisclosure of the U.S. patent application Ser. No. 14/757,749 is herebyincorporated by this reference in its entirety for all of its teachings.The application Ser. No. 14/757,749 is a continuation application andclaims priority to the U.S. patent application Ser. No. 13/744,415 (nowpatented with U.S. Pat. No. 9,247,869) titled “Compact FoldableApparatus for Ophthalmology” filed on 18 Jan. 2013. The entiredisclosure the U.S. patent application Ser. No. 13/744,415 is herebyincorporated by this reference in its entirety for all of its teachings.U.S. patent application Ser. No. 13/744,415 claims priority toprovisional U.S. patent application 61/587,132 titled “A CompactFoldable Apparatus for Ophthalmology”, filed on 17 Jan. 2012 by theinventors Manmohan Singh Sidhu and Manish D. Kulkarni. This benefit isclaimed under 35. U. S. C. $119 and the entire disclosure of theProvisional U.S. patent Application No. 61/587,132 is incorporated hereby reference.

FIELD OF TECHNOLOGY

The following description relates to a system, and an apparatus forophthalmology. The device can be used for diagnosis, evaluation ortherapy. The device can be used for ophthalmic imaging and/or diagnosis,anterior segment imaging and/or diagnosis, retinal imaging and/ordiagnosis. The apparatus and system can be used for the eyes of thehumans as well as the animals.

BACKGROUND

Most of the ophthalmic systems comprise of the chin-rests that are notfoldable. A patient, (whose eye needs to be examined), rests his/herchin on this chin-rest so that the eye can be stabilized for usefulmeasurements on the eye. While useful for stabilizing the patient's eye,these chin-rests form a significant part of the device's footprint. Sucha chin-rest is a significant hurdle for minimizing thedevice-form-factor, and building an apparatus or a system that iscompact and portable. European patent (publication number EP1441640 A2and EP1441640A4, filed Oct. 16, 2002 by E. Ann Elsner) discusses afoldable head or chin-rest. However it does so very briefly withoutproviding design details and only in the context of digital imaging ofthe retina and anterior segment. It does not discuss optical coherencetomography/optical coherence domain reflectometry (OCDR). Proposeddesign is more detail, generic and all-inclusive of various ophthalmicmodalities.

SUMMARY

The invention discloses a foldable system, and a foldable apparatus forophthalmology. The apparatus and system can be used for diagnosis,evaluation or therapy. The device can be used for ophthalmic imagingand/or diagnosis, anterior segment imaging and/or diagnosis, retinalimaging and/or diagnosis. The apparatus and system can be used for theeyes of the humans as well as the animals. In the proposed system, thechin-rest can be folded to save the space when the device is not inoperation. This saves space while the device is in storage or undertransportation.

In one embodiment, the apparatus or system comprises of an ophthalmicsystem comprising of at least one means to hold the face of a patient(i.e., face-holder), a diagnostic component to perform diagnosis orevaluation of the eye or a therapeutic component for the treatment ofthe eye and the means to fold the face-holder. Such a device can betermed as a “foldable face-holder apparatus” or a “foldable face-holdersystem”.

In another embodiment, the face-holder can be folded at least once andpossibly multiple times.

In another embodiment the face-holder comprises of a resting pad to restthe forehead (i.e., forehead rest).

In another embodiment, the face-holder comprises of a resting pad torest the chin (i.e., chin-rest).

In another embodiment, the face-holder can be folded by collapsingmulti-stage telescopic legs.

In another embodiment, the face-holder comprises of a chin-rest and aforehead rest and only the portion between the chin-rest and theinstrument base is collapsible using multi-stage telescopic legs.

In another embodiment, the face-holder comprises of a chin-rest and aforehead rest and only the portion below the chin-rest and theinstrument base is collapsible using multi-stage telescopic legs.

In one more embodiment, there is a folding hinge at or near thechin-rest.

In an embodiment, there is a folding hinge for the face holder at ornear the instrument base.

In another embodiment, the proposed ophthalmic system comprises of atleast one means to hold the face of a patient (i.e., face-holder) andthe means to eject or remove the face-holder from the base of theinstrument.

In another embodiment, the chin-rest can be removed or ejected using abutton from the base of the instrument.

In another embodiment, the chin-rest is attached to the base of theinstrument. In some other embodiments, the chin-rest-attachment isremovable.

In another embodiment, the chin-rest is attached to the pole of theface-holder. and the chin-rest can be ejected or removed from the poleof the face-holder.

In one more embodiment, an ophthalmic system comprises of at least onemeans to hold the face of a patient (i.e., face-holder), an oculardiagnostic or therapeutic component and the means to remove theface-holder from the instrument and attach it to the patient's face.

In another embodiment, the face-holder is attached to the eyes using ahead-band. In some embodiments, face-holder comprises of a chin-rest.

In some other embodiments, the face-holder is attached to the eyes usingspectacles-type assembly. The eye-piece may be moved from one eye to theother for analyzing both the eyes.

In some embodiments, the chin-rest and/or the face-holder can slide inand out from the side of the ophthalmic system's base.

In some embodiments, the chin-rest and/or the face-holder can be foldedcompletely and slides in the instruments' system's side.

In some embodiments, the apparatus or the system comprises of ophthalmicimaging.

In some other embodiments, the apparatus or the system comprises ofoptical coherence tomography (OCT) imaging.

In some other embodiments, the foldable face-holder apparatus or systemcomprises of optical coherence tomography (OCT) imaging apparatus/systemand the OCT apparatus/system comprises of a spectrometer to implementspectral-domain OCT.

In some other embodiments, the foldable face-holder apparatus comprisesof optical coherence tomography (OCT) imaging apparatus/system and theOCT apparatus/system comprises of a tunable wavelength (or frequency)light source to implement swept-source OCT or optical frequency domainreflectometry (OFDR).

In some other embodiments, the foldable face-holder apparatus or systemcomprises of optical coherence tomography (OCT) imaging apparatus/systemand the OCT apparatus/system comprises of a depth-scanning referencemirror to implement time-domain OCT.

In one embodiment, the OCT system and apparatus mentioned abovecomprises of a light source of specific bandwidth, isolator, beamsplitter, optical delivery unit, specimen, a grating, a detector arrayand a processor containing specific algorithms for signal and/or imageprocessing.

In another OCT embodiment, as an additional feature, a polarizationcompensator is added to the basic configuration mentioned above. In oneembodiment, a fiber stretcher is added in the basic configuration. Thefiber stretcher is used to adjust the path-length in the correspondingarm of the system.

In one embodiment, the foldable system comprises of an OCT systemcomprising of a light source, provides a broad band light (of specificbandwidth) for acquiring an image from the subsurface area of aspecimen. The specimen may be, but not limited to a moving sample, astationary sample or a combination of both. The specimen may be a humanor an animal eye or a device similar to an eye. In another embodiment,the system is modular so that a user can add off-the-shelf products toenhance the system capabilities. In another embodiment, severalcombinations of the basic configuration and additional components may beadded to enhance the performance of the apparatus as a system as shownin the various figures that accompany this application, but not limitedto only those.

In another embodiment, specific algorithm(s) reside in a processor inthe foldable system to create an OCT image. The processor uses thealgorithms such as the frequency resampling, demodulation, dispersioncompensation, and Doppler processing to produce highly sensitive andhigh quality images. In another embodiment, the system performsspectroscopic detection. The resultant spectra are analyzed by theprocessor using inverse Fourier transformation and relevant signalprocessing for obtaining depth dependent (i.e. axial) reflectivityprofile called A-scan. In another embodiment, two dimensionaltomographic images, B-scan, are created from a sequence of axialreflectance profiles acquired by scanning the specimen.

In one embodiment, the foldable system may comprise of an OCT/OCDRsub-system comprising of a light source, an isolator, a processor, afiber stretcher, a source arm, a reference arm, a sample arm, adetection arm, a beam splitter, a detector array, a grating unit, anoptical delivery unit which can be folded, and a specimen (e.g., an eye)for analysis.

In some embodiments, bulk of the OCT/OCDR sub-system, e.g., lightsource, an isolator, a processor, a fiber stretcher, a source arm, areference arm, a sample arm, a detection arm, a beam splitter, adetector array, a grating unit resides in the base of the foldablesystem.

In another embodiment, an OCT/OFDR sub-system may comprise of a tunablelight source, an isolator, a processor, a fiber stretcher, a source arm,a reference arm, a sample arm, a detection arm, a beam splitter, adetector, an analog-to-digital converter, an optical delivery unit, anda specimen (e.g., human or animal eye) for analysis. In someembodiments, a polarization compensator may be used on the sample and/orreference arm. In some embodiments, the bulk of the OFDR/OCT componentsreside in the base of the foldable system.

In another embodiment, the OCT/OCDR sub-system enables a user to adjustthe reference arm and the sample arm in order to adjust the path-lengthsand/or polarization of the light beam to get a better quality image.

In another embodiment, light from a broadband light source operating ata suitable center wavelength is sent to an isolator, and then to thebeam splitter using the source arm of the OCT sub-system. In anotherembodiment, the beam splitter splits the broadband light into two parts.One part of the light beam goes to the reference mirror using the fiberstretcher (on the reference arm) and other beam goes to the specimenusing the sample arm.

In some other embodiments, the apparatus/system comprises of means toshift the eye-piece (which is optics used to focus on the eye) towardsthe left or right eye.

In some embodiments, the eye-piece is shifted using a precision slide.

In some other embodiments, the eye-piece is shifted using a sliding rod.

In some embodiments, the eye-piece is positioned using a micro-precisionslide.

In some embodiments, the foldable face-holder apparatus/system comprisesof the means for an eye-fixation target.

In some embodiments, the apparatus/system comprises of fiber or cablesrunning from the instrument to the eye.

In another embodiment, the OCT sub-system mentioned above has also atleast one of a fractional wave mirror, waveplate (e.g., λ/8), afiber-optic mirror and a free space mirror.

In some embodiments, the apparatus/system comprises of a screen todisplay measurement or imaging results.

In some other embodiments the display screen is a touch-sensitivescreen.

In some embodiments, the base of the apparatus/system comprises ofelectronics and optical components.

In some embodiments, all the apparatus or system components reside in abrief-case or a suit-case or a box or a tablet (e.g., an iPad or androidtablet)-size unit.

In some embodiments, the brief-case has wheels and/or a handle to assisttransportation.

In some embodiments, the apparatus/system operates on batteries. In someother embodiments, these batteries can be rechargeable batteries. Thebatteries can be charged independently or by connecting a charger to theapparatus/system. The charger can source power from the electricalwiring in a building or any other power source. The charger can alsosource power from a vehicle such as a car or a bus or a truck or a van.The charger can also source the power from the vehicle's engine.

In some embodiments, the apparatus/system evaluates or scans the retinaand/or the posterior segment. In some other embodiments, theapparatus/system evaluates or scans the cornea and/or anterior segment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a simplified version of the foldable ophthalmicapparatus/system 100.

FIG. 2 depicts the folded version of the foldable ophthalmicapparatus/system 100.

FIG. 3 illustrates telescopic legs.

FIG. 4 is a block diagram of an OCDR-OCT sub-system 400 (which can beincorporated into a foldable ophthalmic system), in accordance with anembodiment of the present invention; the key elements being a gratingunit, a fiber optic mirror, and a fiber stretcher.

FIG. 5 is a block diagram of the OCDR-OCT system 500 (which can beincorporated into a foldable ophthalmic system) similar to that in FIG.4 except that the fiber optically integrated mirror is replaced by afree space mirror.

FIG. 6 is a block diagram of the OFDR (optical frequency domainreflectometry)-OCT system 600 (which can be incorporated into a foldableophthalmic system) similar to that in FIG. 4 except that the broad-bandsource is replaced by a tunable frequency source, detector array isreplaced by a single high-speed detector, and the diffraction grating iseliminated. Such a system is called swept-source OFDR/OCT.

FIG. 7 is a block diagram of the OFDR-OCT system 700 similar to that inFIG. 6 except that the fiber optically integrated mirror is replaced bya free space mirror. This system can be incorporated into a foldableophthalmic system.

FIG. 8 is a block diagram of the OFDR-OCT system 700 without the fiberstretcher. The mirror in the reference arm is able to move back andforth. This system can be incorporated into a foldable ophthalmicsystem.

FIG. 9 is a flow chart describing a method of acquiring an image from aspecimen using the OCDR-OCT system.

FIG. 10 is a flow chart of a method describing the usage of theapparatus.

FIG. 11 is a flow chart of methods of the signals and images beingprocessed from the start to finish.

FIG. 12 is a flow chart of a method of demodulating the signal torecover the complex envelope of the OCT/OCDR/OFDR signal.

FIG. 13 is a flow chart of a method of Doppler processing the signal toestimate the Doppler shift and the corresponding velocities of theparticles in the specimen.

DETAILED DESCRIPTION

The instant disclosure describes a technological advancement of foldableophthalmic apparatus and system. Such a system would be compact,portable and would save storage space.

FIG. 1 depicts a simple version of the foldable face-holderapparatus/system 100. The apparatus/system comprises of an ophthalmicsystem comprising of at least one means to hold the face of a patient(i.e., face-holder 102), a diagnostic component to perform diagnosis orevaluation or a therapeutic component to perform treatment of the eyeand the means to fold the face-holder (e.g., hinge 114). Thus theapparatus and system will comprise of at least one of diagnostic,evaluation and therapeutic components.

The diagnostic, evaluation and/or therapeutic components can directlight to the eye (and receive the back-scatter from the eye) using anoptical delivery unit. In some embodiments, the optical delivery unit isa part of the face-holder.

In some embodiments, the face-holder can be folded at least once andpossibly multiple times. In some embodiments, the face-holder comprisesof a resting pad to rest forehead (i.e., forehead rest 110). In anotherembodiment, the face-holder comprises of a resting pad to rest chin(i.e., chin-rest 104).

In another embodiment of the instant apparatus or system, theface-holder can be folded by collapsing multi-stage telescopic legs. Inanother embodiment, the face-holder comprises of a chin-rest 104 and aforehead rest 110 and only the portion between the chin-rest 104 and theinstrument base 118 is collapsible using multi-stage telescopic legs(FIG. 3).

In some other embodiments, the apparatus/system comprises of aneye-piece 112 which is optics and mechanics used to evaluate or treatthe eye. In some embodiments, the eye-piece is a part of the opticaldelivery unit.

In some embodiments, the apparatus/system comprises of a screen 106 todisplay measurement or imaging results. Thus, the display can hostdiagnostic-assisting results. In some other embodiments the displayscreen 106 is a touch-sensitive screen. In some other embodiments, thedisplay could have 3-D capabilities (or stereoscopic capabilities)showing 3-dimensional features of the data or the measurements oranatomic features.

In some embodiments, the apparatus/system comprises of a keyboard 108 tocontrol the apparatus/system. The keyboard 108 can optionally compriseof a mouse or a controlling ball or a joystick. In some otherembodiments the keyboard 108 is a touch-sensitive screen. In someembodiments, the touch-sensitive display comprises of the keyboard.

In some embodiments, the eye-piece is shifted using a precision slide toevaluate or treat the left or right eye. In some other embodiments, theeye-piece is shifted using a sliding rod. In some embodiments, theeye-piece is positioned using a micro-precision slide. In someembodiments, the eye-piece is a part of the optical delivery unit.

In some embodiments, the eye-piece has railings to move it forwardand/or backward with respect to the patient's eye.

In some embodiments, the foldable face-holder apparatus/system comprisesof the means for an eye-fixation target. These means could comprise of adisplay inside the eye-piece 112. The display could have an eye-fixationtarget as desired by the operator of the apparatus/system.

In some embodiments, the base 118 of the apparatus/system comprises ofelectronics and optical components. In some other embodiments of theinvention, the apparatus/system comprises of fibers or cables runningfrom the base 118 to the eye-piece 112.

FIG. 2 depicts the folded version of the foldable face-holderapparatus/system 100. It is folded at the hinge 114. In someembodiments, the face-holder can be folded at least once and possiblymultiple times. In another embodiment of the instant apparatus/system,the face-holder can be folded by collapsing multi-stage telescopic legs.In another embodiment, the face-holder comprises of a chin-rest 104 anda forehead rest 110 and only the portion between the chin-rest 104 andthe instrument base 118 is collapsible using multi-stage telescopic legsas illustrated in FIG. 3. The collapsed legs are shown as 302 andelongated legs are shown as 304 in FIG. 3.

In one more embodiment, there is a folding hinge 114 at or near thechin-rest 104.

In another embodiment, the proposed ophthalmic system comprises of atleast one means to hold the face of a patient (i.e., face-holder) andthe means to eject (using a button) or remove the face-holder from thebase of the instrument.

In another embodiment, the chin-rest can be removed or ejected from thebase of the instrument. In another embodiment, the chin-rest is attachedto the base of the instrument. In some other embodiments, thechin-rest-attachment is removable.

In some embodiments, all the apparatus/system components reside in abrief-case as shown in FIG. 1. In some embodiments, the brief-case haswheels and/or a handle to assist transportation.

In some embodiments, the apparatus/system operates on batteries. In someother embodiments, these batteries can be rechargeable batteries. Thebatteries can be charged independently or by connecting a charger to theapparatus. The charger can source power from the electrical wiring in abuilding. The charger (termed a vehicle charger) can also source powerfrom a vehicle such as a car or a bus or a truck or a van. The chargercan also source power from the vehicle's engine.

In some embodiments, the apparatus/system could comprise of a projector(sometimes termed pico-projector) to display the results or the imagesor the data on a wall or a screen.

In some embodiments, the apparatus is used for ophthalmic imaging.Ophthalmic imaging includes (but does not limit to) retinal imaging andanterior segment.

OCT/OCDR/OFDR Sub-System Description

In some other embodiments, the foldable ophthalmic apparatus/systemcomprises of optical coherence tomography (OCT) imaging. Opticalcoherence domain reflectometry (OCDR) is a 1-dimensional measurementsystem and OCT is a 2-D extension of OCDR. Since OCT and OCDR aresimilar, sometimes we would refer these as OCT-OCDR systems. Thediagnostic components or systems based on OCT-OCDR, will be called asOCT-OCDR based diagnostic components.

Optical coherence tomography (OCT) and OCDR are very similar toultrasound imaging. OCDR-OCT provides cross-sectional images ofmicro-features that are acquired from adjacent depth resolvedreflectivity profiles of the tissue. OCT also employs a fiber opticallyintegrated Michelson interferometer illuminated with a short coherencelength light source such as a superluminiscent diode (SLD). Theinterferometric data are processed in a processor/computer and displayedas a gray scale image. In an OCDR-OCT image, the detectable intensitiesof the light reflected from human tissues range from 10⁻⁵ to 10⁻¹¹thpart of the incident power.

In some other embodiments, the foldable face-holder apparatus or systemcomprises for optical coherence tomography (OCT) imagingapparatus/system and the OCT apparatus/system comprises of aspectrometer to implement spectral-domain OCT.

OCDR-OCT System: FIG. 4 shows an OCDR-OCT system 400 comprising of alight source 405 of a specific bandwidth, isolator 421, processor 414,fiber stretcher 412, source arm 401, reference arm 402, sample arm 403,detection arm 404, beam splitter 406, detector array 410, a grating unit413, optical delivery unit 408, fiber optic mirror 417 and a specimen407 (could be a human or an animal eye) for analysis.

In some embodiments, the optical delivery unit 408 is further integratedwith the face-holder of the folding ophthalmic system.

A light source 405, in a system or as a part of the apparatus/system,may comprise of off-the-shelf light sources.

The center wavelength (λ₀) most ideal for the retinal applications rangefrom 750 nm till 1050 nm. Water (and aqueous humor) absorption isminimal for this wavelength range. The power for retinal applicationsranges from 0.1 mW to 10 mW. Per ANSI safety standards only 0.75 mW arepermitted incident on the eye at this wavelength range of 750 nm till850 nm. The center wavelength most ideal for the non-retinalapplications (e.g., skin, anterior segment of the eye, gastrointestinaltract, lungs, teeth, blood vessels, subsurface area of semi-conductors,chip manufacturing, sensitive medical equipment's etc.) range from 1050nm till 1350 nm. The longer wavelength is more suitable for thickscattering tissues since scattering is less at higher wavelengths. Thesystem depth resolution (DR) is inversely proportional to the FWHMspectral width (or bandwidthΔλ) of the light source spectrum. It isgiven by the following equation:

$\begin{matrix}{{D\; R} = {\frac{2\;\ln\; 2}{\pi}\frac{\lambda_{0}^{2}}{\Delta\;\lambda}}} & \left( {{Eq}\mspace{14mu} 1} \right)\end{matrix}$

The full-width-half-max (FWHM) spectral width of the light sourcetypically ranges from 10 nm till 150 nm. The power for non-retinalapplications ranges from 0.1 mW till 30 mW in the wavelength range from1050 nm till 1350 nm. The full-width-half-max (FWHM) spectral width ofthe light source typically ranges from 10 nm till 150 nm.

The light source 405 may be electrically operated. These can be batteryoperated while in transit. The forward voltage typically ranges from 2to 10 Volts. The forward current typically ranges from 100 mA to 1 A.Some of these sources need to be thermo-electrically controlled (TEC).The operating internal temperature for some sources is typically 25° C.The corresponding thermistor resistance is 10 kilo-Ohms (10 kΩ). TypicalTEC current is 1.5 A. Typical TEC voltage is 3-4V. The light source mayalso be tunable light source as shown in other system/apparatusembodiments.

The isolator 421 protects the light source from back reflections andpermits the transmission of light in the forward direction with alimited loss. The fiber-optic isolator used in device would need tooperate on a broad range of spectrum to cover the full spectral-width ofthe light source (Depending upon the source spectral shape, typically2*FWHM bandwidth Δλ). Thus the operating wavelength range is λ₀+/−Δλ.Typical isolation is 20-40 dB, and insertion loss is 0.5-3 dB. Thepolarization dependent loss is typically 0.5 dB or less. Return loss istypically more than 40 dB.

The isolator 421 comprises of an input linear polarizer, a (λ/8) Faradayrotator or a waveplate, and an output linear polarizer. The (λ/8)Faraday rotator or a waveplate rotates the light transmitted through theinput polarizer by 45 degrees. The output polarizer needs to have thesame direction as “the input polarizing direction rotated by 45 degrees”in order to have the maximum transmission and maximum isolation. Thelight returning to the isolator from the remaining system gets linearlypolarized by the output polarizer and is rotated by 45 degrees, makingit orthogonally polarized as compared to the input polarizing direction.Thus, the returning light is totally absorbed.

Fiber stretcher 412 comprises of a fiber looped around a piezoelectricdevice (which is a solid block that can be expanded or contracted byelectric voltage). The fiber stretcher is not strictly necessary in anOCDR/OCT system, it can be optionally used. The purpose of a fiberstretcher is to increase or decrease the path-length in theinterferometer by increasing or decreasing the fiber-length. Althoughthe fiber stretcher 412 is shown in the reference arm, it can be placedether in the reference arm or sample arm. If the fiber stretcher 412 iskept in the reference arm, since the fiber is looped around thepiezoelectric device, care must be taken to provide extra fiber in thesample arm so that the sample arm and reference arm path lengths arematched.

The fiber optic mirror 417 is situated on the tip of the fiber.

Bulk of the components of the OCT/OCDR system can be placed in the baseof the foldable ophthalmic system in some embodiments. The opticaldelivery unit 408 in the sample arm can focus light on the eye, and canbe folded as needed. The optical delivery unit 408 can be attached tothe face holder in some embodiments.

Detector array 410 is a line-scan camera. It has typically 1024-4096pixels, though the proposed embodiment is not limited to these numbers.Typically it is a CCD or CMOS camera. Line-rate (rate of acquisition ofarrays) is typically 10000 lines/s to 400000 lines/s, though theproposed embodiment is not limited to these numbers. Each pixel outputsa value which typically has an 8-bit or 12-bit format, though theproposed embodiment is not limited to these numbers. The pixel size istypically 14 microns (height) and 14 microns (width). The lightdispersed by the grating is focused on the detector array to generatethe light spectrum. The output of the array (line-scan camera) istypically directed to the computer using an Ethernet cable (e.g.,Gigabit Ethernet) or a USB (typically 2.0 or 3.0) cable, etc. Theoperating wavelength ranges from 400 nm to 1100 nm for retinalapplications. The above numbers and examples are given for illustrativepurposes only, the proposed embodiment is not limited to these numbersor examples.

The beam splitter 406 (made of fiber optics) splits the light typicallyinto 50/50. It is built using two fused single-mode fibers. The fiberfor retinal applications (˜800 nm wavelength) has 4-6 microns corediameter and 125 microns cladding diameter, 0.130 core numericalaperture (NA), cutoff wavelength of typically 730 nm. The insertion loss(in addition to designed 3 dB or 50% loss) is typically 0.3 dB. For thecouplers used for OCT, the length of the fiber in the reference andsample arms is very important and the lengths are specified with tighttolerances.

The waves reflected back from the sample arm 403 and the reference arm402 interfere at the detector array 410. Since the interference signalis only created when the polarization in the reference arm 402 matcheswith that in the sample arm 403, in some embodiments, a polarizationcompensator 420 is used either in the reference arm or the sample arm.Polarization compensator 420 is also known as fiber optic polarizationcompensators. In some embodiments, the compensator comprises of 3 coilsof fiber on 3 different paddles arranged in a series. The first fibercoil is a quarter wave plate, the second fiber coil is a half wave plate(typically the fiber is looped around twice for the same paddle diameteras the first paddle), the last fiber coil is a quarter wave plate. These3 paddles can be rotated freely with respect to each other to produceany polarization state.

There is another type of polarization compensator, which appliespressure to the fiber to create birefringence. The slow axis is in thedirection of the pressure applied. This fiber squeezer can be rotatedaround the fiber to rotate the direction of the slow axis. Thus, anyarbitrary polarization can be created.

In some embodiments of the OCT systems, light exits a fiber tip in thereference arm and the light returns from a retro reflecting mirrormounted in the air.

OCDR-OCT sub-system uses spectroscopic detection method. Basically theinterferometric light exiting the detector arm 403 is dispersed via agrating. The spectra are acquired using a line-scan camera. Theresulting spectra are typically (by way of example, not by limitation)transferred to a processor for inverse Fourier transforming and relevantsignal processing (such as obtaining the complex envelope of theinterferometric signal) for obtaining depth dependent (i.e., axial)reflectivity profiles (A-scans). The axial resolution is governed by thesource coherence length, typically ˜3-10 μm. Two dimensional tomographicimages (B-scans) are created from a sequence of axial reflectanceprofiles acquired while scanning the probe beam laterally across thespecimen or biological tissue.

A-scan: A-scan is a plot of reflectivity of scatterers and layers as afunction of depth at a given lateral location. It is computed asfollows:

-   a) The interferometric light exiting the detector arm is dispersed    via a grating.-   b) The dispersed light has a spectrum which is focused on a detector    array or a line-scan camera. Thus, the grating unit disperses the    partial returning light from the beam splitter and a dispersed light    enters the detector array to produce a light spectrum.-   c) The recorded spectra are typically transferred to a processor.    The processor performs a data analysis using specific algorithms on    the light spectrum.-   d) An inverse Fourier transform of the spectrum is computed.-   e) Relevant signal processing is performed (such as removing the    duplicate data and strong spikes at the center of the inverse    Fourier transform) using specific algorithms.-   f) The resulting arrays are depth dependent (i.e., axial)    reflectivity profiles (A-scans). Thus the system generates A-scans    of the eye; if the eye is the specimen used in the system.-   g) The axial resolution is governed by the source coherence length,    typically ˜3-10 μm.

B-scan: Two dimensional tomographic images (B-scans) are created from asequence of axial reflectance profiles acquired while scanning the probebeam laterally across the specimen or biological tissue. The followingare detail steps:

-   a) An A-scan is acquired at a given lateral location.-   b) A mirror is scanned using a scanner such as a galvanometer or a    MEMS mirror in the optical delivery unit.-   c) Multiple A-scans are acquired at various lateral locations.-   d) A matrix is generated where columns indicate different lateral    locations and rows indicate reflectivity at each depth in each    A-scan.-   e) The matrix is displayed as an image, which is also a B-scan.

In some embodiments of this invention, the grating disperses light and alens focuses it into a detector array 410. By way of example, but not bylimitation, this array can be a line-scan camera, which has quantumefficiency p at the operating wavelengths. The resulting data set isinverse Fourier transformed, processed in a processor 414 and displayedas a gray scale or pseudo-color image. By way of example, not bylimitation, this processor can be a computer, off-the-shelf integratedcircuit, application specific integrated circuit (ASIC), FieldProgrammable Gate Array (FPGA), a graphical processing unit (GPU) anembedded system or a microcontroller.

Extensions of the proposed interferometer: An interferometric 2D imagingsystem (Optical coherence tomography or OCT) can be constructed usingthe proposed interferometric system where the 2D images are obtained bylaterally scanning the beam incident on the sample using a 1-D scanningmirror (which is a part of the optical delivery unit). Aninterferometric 3D imaging system can be constructed using the proposedinterferometric system where the 3D data-sets are obtained by 2Dlaterally scanning the beam incident on the sample using a 2-D scanningmirror (which is a part of the optical delivery unit).

Both the 2D imaging systems and 3D imaging systems can be adapted forophthalmic imaging by using a lens assembly (which is a part of theoptical delivery unit) to focus the light on the retina.

In some embodiments, the optical delivery unit is integrated with theface-holder of the foldable ophthalmic system.

An example lens assembly is described below (not as a limitation), butother lens assemblies could be used. The OCDR-OCT system can be adaptedto measure retina by collimating the beam exiting the sample arm fiber,expanding the beam using a lens, shrinking the beam to project on thecornea, and the cornea and lens system of the eye will automaticallyfocus the beam on the retina.

In some embodiments, a fractional wave mirror is placed at the end ofthe reference arm of the OCDR/OCT/OFDR system. The fractional wavemirror comprises of a fiber-optic mirror preceded by a fractional [45degrees (λ/8)] waveplate. Here λ indicates wavelength. The polarizationof light incident on the wave plate is rotated by 45 degrees, and isdirected to the fiber-optic mirror. The reflected light is furtherrotated by 45 degrees by the fractional [45 degrees (λ/8)] waveplate andhence the resulting polarization is orthogonal to the incidentpolarization. Polarization compensator 420 may not be necessary in thisembodiment. A modified formula based on LeFevre is disclosed in thisdisclosure and which is as follows:

Mechanical stress on the fiber causes birefringence in the fiber. Stresscan be generated by simply bending the fiber. According to LeFevre (U.S.Pat. No. 4,615,582), the fractional wave plate can be built by loopingthe fiber into N loops having a radius R. The refractive indexdifference Δn for two orthogonal polarizations is given by

$\begin{matrix}{{\Delta\; n} = {b\left( \frac{r}{R} \right)}^{2}} & \left( {{Eq}\mspace{14mu} 2} \right)\end{matrix}$b is a constant depending upon the photoelastic coefficient of thefiber, r is the radius of the fiber and R is the radius of the fiberloop. Thus, if we want to create a λ/m (where m is an integer)waveplate, which will introduce a path-length shift of λ/m between 2polarizations, we'll need to create a loop of fiber length L to createthe path-length shift of ΔnL. However, since the length of the fiber isalso equal to 2πNR, where N is the number of loops, we get

$\begin{matrix}{{\left( {2\;\pi\;{NR}} \right){b\left( \frac{r}{R} \right)}^{2}} = \frac{\lambda}{m}} & \left( {{Eq}\mspace{14mu} 2} \right) \\{or} & \; \\{R = {\left( {2\;\pi\;{mN}} \right)b\frac{r^{2}}{\lambda}}} & \left( {{Eq}\mspace{14mu} 4} \right)\end{matrix}$To create a fractional wave plate of

$\frac{\lambda}{8},$and N=1 (single loop), b=0.25, m=8, r=125 microns, λ=0.8 microns, we get

$\begin{matrix}{R = {{\left( {2\;\pi\; 8} \right)0.25\frac{(125)^{2}}{0.8}} = {{5\;\pi*15625} = {24.54\mspace{14mu}{cm}}}}} & \left( {{Eq}\mspace{14mu} 5} \right)\end{matrix}$Please note that a (2M+1)λ/m waveplate where M is an integer between −∞to ∞ will have a similar effect as a λ/m waveplate. The correspondingequation is

$\begin{matrix}{R = {\left( {2\;\pi\;{mN}} \right)b\frac{r^{2}}{\lambda\left( {{2M} + 1} \right)}}} & \left( {{Eq}\mspace{14mu} 6} \right)\end{matrix}$Thus, if M=5 in the example above; R would be 2.23 cm, leading to a morecompact loop. We could choose various values of M leading to an optimaldesign and size.

The waves reflected back from the sample arm 403 and the reference arm402 interfere at the detector array 410. Since the interference signalis only created when the polarization in the reference arm 402 matcheswith that in the sample arm 403, in some embodiments, one can include byway of example but not by limitation a 45 degrees λ/8 waveplate in thesample arm 403 just before the light is incident on the optical deliveryunit 408. Since the polarization of the retro reflected light will bealmost orthogonal to the incident light (considering the fact that thebirefringence in the specimen 407 will modify the polarization state),the birefringence effects in the sample arm fiber 403 of theinterferometer 400 will get cancelled. In an embodiment, the λ/8waveplate is constructed using fiber optic components.

In another preferred embodiment, the λ/8 waveplate is afractional-waveplate constructed using fiber optic components. It wouldbe constructed in the optical delivery unit near the end of the fibersegment in the optical delivery unit. The fractional waveplate islocated on the sample arm of the apparatus/system. It may be made anintegral part of the optical delivery 408. The fractional wave mirror inthe reference arm comprises of a fiber-optic mirror preceded by afractional [45 degrees (λ/8)] waveplate. The polarization of the lightincident on the waveplate is rotated by 45 degrees, and is directed tothe mirror. The reflected light is further rotated by 45 degrees by thefractional [45 degrees (λ/8)] waveplate and hence the resultingpolarization is orthogonal to the incident polarization. In anotherembodiment, a free-space-bulk 45 degrees (λ/8) wave plate is used at theend of the optical delivery unit. Polarization compensator 420 may notbe necessary in these embodiments.

In some embodiments, the optical delivery unit 408 in the sample arm isintegrated with the foldable face-holder.

In another variation of this embodiment (system 500 in FIG. 5), thefiber optically integrated mirror can be replaced by a free space mirror518. The light can be delivered to the mirror using optical deliveryunit 519. FIG. 5 has standard free-space-mirror 518 in the referencearm, which still permits use of instant algorithms such as frequencyresampling, dispersion compensation, and Doppler processing algorithms.In some embodiments, the foldable face-holder comprises of the opticaldelivery unit 408 in the sample arm.

In some other embodiments, the foldable face-holder system is used foroptical coherence tomography (OCT) imaging and the OCT system comprisesof a tunable wavelength (or frequency) light source to implementswept-source OCT or optical frequency domain reflectrometry (OFDR) (asdescribed in S R Chinn, E A Swanson, J G Fujimoto—Optics Letters, 1997;M A Choma, M V Sarunic, C Yan et al—Optics Express, 2003; Y Yasuno, V DMadjarova, S Makita, M Akiba et al—Optics Express 2005).

Frequency Domain OCT or swept source OCT or Optical Frequency DomainReflectometry (OFDR): In some OCT sub-systems such as frequency domainOCT or swept source OCT or Optical Frequency Domain Reflectrometry(OFDR), the broad-band light source is replaced by a tunable frequencylight source. The detector array is replaced by a single detector. Theuse of a grating is not needed for this embodiment. In this embodiment(system 600 in FIG. 6), a fiber-optically integrated mirror 417 in thereference arm 402 of the OFDR-OCT system 600 can be used. Tunable lightsource 602 in this embodiment is applicable to FIG. 6-8 only. The centerwavelength most ideal for the retinal applications range from 750 nmtill 1050 nm. The wavelength of the source is tuned very rapidly (e.g.,at a rate of 10 kHz-10 MHz) within a spectral range of typically 10 to100 nm around the center wavelength. The average power of such a sourcetypically ranges from 0.1 mW to 20 mW depending upon the applications.The source may be electrically operated. The existing commerciallyavailable sources operate on 110/220V 50/60 Hz power input. In future,these could be operated using lower voltages and battery operated whilein transit. ADC 624 is added so that the electrical current istransformed.

In this embodiment there is no grating 413 and detector array. Instead aDetector 622 is added. It is a photo-diode (which converts light intoelectricity). The detectors for 300-1000 nm are typically made up ofsilicon. The detectors for 900-1700 nm are typically made up of InGaAs.These are high-speed detectors with typically 0 to a few hundred MHzbandwidth. In some embodiments more than one detector may be used toachieve dual-balanced detection. It is typically followed by ahigh-speed A/D (analog to digital) converter (ADC) 624, e.g., 8-bit or12-bit with a conversion rate of 1 to 20000 Mega Samples/second. Thedetector(s) direct(s) the signal to the ADC to generate a digitizedsignal. Typical responsivity of photodiodes is 0.1-1 mA/mW. The outputvoltages are typically −5 to 5V, with typical 50Ω impedance. Theseassist in achieving typical line-rates (rate of acquisition of A-scans)of 10000 lines/s to 400,000 lines/s (can be higher than 10 M lines/s invery high speed lasers). The digitized output of the A/D converter istypically directed to a computer or a processor using an Ethernet cable(e.g., Gigabit Ethernet) or a USB (typically 2.0 or 3.0) cable, ordirectly attached to the computer's PCI (Peripheral ControllerInterface) bus etc. The processor generates A-scans and/or B-scans.

Since the interference signal is only created when the polarization inthe reference arm 402 matches with that in the sample arm 403, in someembodiments, a polarization compensator 420 is used either in thereference arm or the sample arm. Polarization compensator 420 is alsoknown as fiber optic polarization compensator. In some embodiments, thecompensator comprises of 3 coils of fiber on 3 different paddlesarranged in a series.

In some embodiments, a fractional wave mirror (as described earlier) isplaced at the end of the reference arm of the OCT/OFDR system. Thefractional wave mirror comprises of a fiber-optic mirror preceded by afractional [45 degrees (λ/8)] waveplate. Here λ indicates wavelength.The polarization of light incident on the wave plate is rotated by 45degrees, and is directed to the fiber-optic mirror. The reflected lightis further rotated by 45 degrees by the fractional [45 degrees (λ/8)]waveplate and hence the resulting polarization is orthogonal to theincident polarization. Polarization compensator 420 may not be necessaryin this embodiment.

The waves reflected back from the sample arm 403 and the reference arm402 interfere at the detector array 410. Since the interference signalis only created when the polarization in the reference arm 402 matcheswith that in the sample arm 403, in some embodiments, one can include byway of example but not by limitation a 45 degrees λ/8 waveplate in thesample arm 403 just before the light is incident on the optical deliveryunit 408 in the OCT/OFDR system. Since the polarization of the retroreflected light will be almost orthogonal to the incident light(considering the fact that the birefringence in the specimen 407 willmodify the polarization state), the birefringence effects in the samplearm fiber 403 of the interferometer 400 will get cancelled. In anembodiment, the λ/8 waveplate is constructed using fiber opticcomponents. Polarization compensator 420 may not be necessary in thisembodiment.

In another preferred embodiment, the λ/8 waveplate is afractional-waveplate constructed using fiber optic components in theOCT/OFDR system. It would be constructed in the optical delivery unitnear the end of the fiber segment in the optical delivery unit. Thefractional waveplate is located on the sample arm of theapparatus/system. It may be made an integral part of the opticaldelivery 408. The fractional wave mirror in the reference arm comprisesof a fiber-optic mirror preceded by a fractional [45 degrees (λ/8)]waveplate. The polarization of the light incident on the waveplate isrotated by 45 degrees, and is directed to the mirror. The reflectedlight is further rotated by 45 degrees by the fractional [45 degrees(λ/8)] waveplate and hence the resulting polarization is orthogonal tothe incident polarization. In another embodiment, a free-space-bulk 45degrees (λ/8) wave plate is used at the end of the optical deliveryunit. Polarization compensator 420 may not be necessary in thisembodiment. The foldable face holder comprises of the optical deliveryunit 408 in some embodiments.

FIG. 7 is a block diagram of the OFDR-OCT system 700 similar to that inFIG. 6 except that the fiber optically integrated mirror is replaced bya free space mirror 518. The light can be optionally focused on themirror using an optical delivery unit 519. The optical delivery unit 408can be fixed to the foldable face holder in some embodiments.

FIG. 8 is a block diagram of the OFDR-OCT system 700 without the fiberstretcher. The mirror 518 in the reference arm is able to move back andforth to match with the pathlength in the sample arm. The mirror motioncan be achieved by a translation stage or a motorized stage or agalvanometer or a scanner. The foldable face holder comprises of theoptical delivery unit 408 in some embodiments.

Extensions of the proposed interferometer: An OFDR/OCT interferometric2D imaging system can be constructed using the proposed interferometricsystem where the 2D images are obtained by laterally scanning the beamincident on the sample using a 1-D scanning mirror (which is a part ofthe optical delivery unit). An interferometric 3D imaging system can beconstructed using the proposed interferometric system where the 3Ddata-sets are obtained by 2D laterally scanning the beam incident on thesample using a 2-D scanning mirror (which is a part of the opticaldelivery unit).

Bulk of the components of the OCT/OFDR system can be placed in the baseof the foldable ophthalmic system in some embodiments. The opticaldelivery unit in the sample arm can focus light on the eye, and can befolded as needed. The optical delivery unit can be attached to the faceholder in some embodiments.

In some embodiments, the OCT/OCDR/OFDR apparatus/system operates onbatteries. In some other embodiments, these batteries can berechargeable batteries. The batteries can be charged independently or byconnecting a charger to the apparatus. The charger can source power fromthe electrical wiring in a building. The charger (termed a vehiclecharger) can also source power from a vehicle such as a car or a bus ora truck or a van. The charger can also source power from the vehicle'sengine.

Method of Image Acquisition and Analysis

FIG. 9 describes a method of acquiring an image from a specimen usingthe OCDR-OCT sub-system. A light source may be a tunable light source, abroadband source, or a laser. An apparatus or system is used to send aspecific bandwidth light from a light source to a specimen 904 using asource arm and sample arm. A backscattered light from the specimen isreceived 906 by the optical delivery unit. An image is formed 908 aftergoing through the grating and detector array and checked for quality910. If the image quality is poor 912, the steps from 904 are repeated.If the image quality is good 914 data is further sent to produce animage for analysis 916 using the processor algorithms. The process endsonce the image is formed 918. The foldable face-holder comprises of theoptical delivery unit 408 in the sample arm.

FIG. 10 describes the steps of light travelling through the source tothe specimen and the signal from the light being processed. Light isbeing delivered using a light source using the sample arm to the beamsplitter 1004. Beam splitter splits the light into two parts sending thefirst path light to reference arm 1008 and second path light into thesample arm 1010. The second path light goes to the specimen via theoptical delivery unit. The specimen in this case may be a human or ananimal eye. Since the blood flows at irregular intervals and the pictureis not static at times; stationary-object light-backscattering,moving-object-light-backscattering andcombined-object-light-backscattering are returned to the beam splitter.

Sample arm sends the second path of light to the specimen (or the eye)using the optical delivery unit and the specimen (or the eye) reflectsback the second path of light as a returning light via the opticaldelivery unit to the beam splitter 1014. A reference mirror returns thelight into the fiber to be combined with the returning light from thespecimen at the beam splitter 1016. Thus, the reference mirror in thereference arm returns the first path light to the beam splitter to joina returning light from the eye or the specimen. The combined lightsplits in the beam splitter again to go into source and detector arms1018. A partial returning light from the beam splitter travels through adetector arm to a grating unit and a detector array in OCDR-OCT systemor enters the detector if it is OFDR-OCT system to be converted todigitized signal 1020 using analog-to-digital-converter 624. Digitizedsignal enters the processor for A-scan generation and/or image (B-scans)formation 1022. The method ends there 1024. On the other hand partiallight returns to the isolator using the source arm 1026 and the methodends there 1028. The foldable face-holder comprises of the opticaldelivery unit 408 in the sample arm.

FIG. 11 shows a high level flow of the processing algorithms. Step 1102is the beginning step. For the OCDR-OCT system, the spectra are acquiredfrom the detector array as explained earlier (Step 1104). Since theacquired spectra are typically spaced in equal intervals of wavelength,in the step 1106, the spectra are resampled at equal intervals ofspatial frequency (k-space) using a frequency resampling algorithm. Nextin step 1108, demodulation, which includes inverse Fourier transforming,is performed to extract the complex envelope of the signal. Next inorder to correct for the dispersion in the system, the dispersioncompensation is performed in step 1110. Next in step 1112, Dopplerprocessing is performed to extract velocity images. The method ends instep 1114. These algorithms are processed in a processor 114 anddisplayed as a gray scale or pseudo-color image. By way of example, notby limitation, this processor can be a computer, Field Programmable GateArray (FPGA), an embedded system or a microcontroller.

Frequency Resampling: The spectra W_(ccd)(λ,x) measured by thespectrometer (i.e., the output of the digital array) are equally spacedin wavelength (λ). However in order to obtain an accurate A-scanmeasurement by inverse Fourier transforming, the spectra need to bere-measured at equal intervals of spatial frequency (k=1/λ). Thus, if Nis the total number of samples, the spectra are measured at equalintervals in wavelength δλ=(λ max−λ min)/N. The spectra need to beequally spaced in k-space. Thus, if the corresponding maximum andminimum wavenumbers are k max=1/λ min and k min=1/k max, then thespectra need to be re-sampled at equal intervals in k given by δk=(kmax−k min)/N to obtain S_(ccd)(k,x). If the data are over-sampled whilere-sampling by a factor of X, then δk=(k max−k min)/XN.

There are many algorithms for re-sampling the spectra. One such methodis simple linear interpolation as described by [Vergnole et al 2010].Thus, if we need to calculate the spectrum S_(ccd)(k₀,x) at a locationk₀, and the spectra are measured at the nearest neighboring wavenumbersk_(u) (upper wavenumber=1/λ_(u), λ_(u) is the upper wavelength), k₁(lower wavenumber=1/λ₁, λ₁ is the lower wavelength)

${{{Then}\mspace{14mu}{S_{ccd}\left( k_{0} \right)}} = {{S_{ccd}\left( k_{l} \right)} + {U_{0}\left\lbrack {{S_{ccd}\left( k_{u} \right)} - {S_{ccd}\left( k_{l} \right)}} \right\rbrack}}};{U_{0} = \frac{k_{0} - k_{l}}{k_{u} - k_{l}}}$and note that S_(ccd)(k_(l))=W_(ccd)(λ_(l),x)= andS_(ccd)(k_(u))=W_(ccd)(λ_(u),x)

Another method described by [Vergnole et al. 2010] is splineinterpolation. A preferred and faster method of interpolation isachieved by convolution using a Kaiser-Bessel window as described by[Vergnole et al. 2010]. S_(ccd)(k₀)=Σ_(l=−M/2)^(M/2)S_(ccd)(k_(l))C₀(k_(l)) where k_(l) are the non-linearly placedneighboring values of wavenumbers, M is the size of the convolutionkernel. M can be any value, however a value between 3 to 9 can yieldgood results.

${C_{0}\left( k_{l} \right)} = \frac{I_{0}\left( {\gamma\sqrt{1 - \left( \frac{2H}{M} \right)^{2}}} \right)}{M}$where H=smaller of

$\frac{M}{2}$or (k−k_(l))/δk and I₀ is the zero-order Bessel function of the firstkind. To the best of our knowledge, this is the first time a convolutionbased interpolation method is used for the OCDR/OFDR/OCT sub-system,which can be either folded in a suit-case/brief-case or its opticaldelivery unit in the sample arm can be folded.

Next in FIG. 12, we present a novel algorithm such as a demodulationalgorithm (step 1202), which is also instant version of the modifiedHilbert transform algorithm:

-   1) Resampled CCD spectra S_(ccd)(k,x) are obtained as a function of    k (wavenumber) and lateral dimension x (step 1204).-   2) Spectra are Fourier transformed in lateral dimension to obtain    spectra P_(ccd)(k,u) where u is frequency in lateral dimension (step    1206).-   3) The negative frequency signals are zeroed out using Heaviside    function H(u) to provide P′_(ccd)(k,u) (step 1208).-   4) The P′_(ccd)(k,u) is inverse Fourier transformed to obtain    complex spectra S′_(ccd)(k,x) (step 1210).-   5) S′_(ccd)(k,x) is inverse Fourier transformed in k (i.e., depth)    dimension to obtain complex envelop in Eq. 2 (step 1212)    s(z,x)=A(z,x)exp [−j(2πf _(s)(z,x)zT/D+ϕ(z,x))].  (Eq. 6)

Here A(z,x) is the amplitude of the detected signal corresponding to thedepth-resolved reflectivity obtained in conventional OCT imaging andϕ(z,x) is the phase corresponding coherent interference of backscatteredwaves, commonly known as speckle. Here z is the depth location, x is thelateral location, D is total depth of A-scan, T is the time taken toacquire an A-scan. For a broadband source, A(z,x) is a highly localizedfunction (e.g., a Gaussian) whose width determines the axial resolutionof the OCT image. f_(s) is Doppler shift in light backscattered frommoving objects in the sample. A scatterer in the sample moving with avelocity V_(s) induces a Doppler shift in the sample arm light by thefrequencyf _(s)=2V _(s)[cos θ]n _(t) v ₀ /c  (Eq. 7)where θ is the angle between the sample probe beam and the direction ofmotion of the scatterer, n_(t) is the local tissue refractive index, v₀is the source center frequency, and c is the light velocity.

Dispersion compensation: Group velocity dispersion needs to be matchedbetween the reference and sample arms. In some embodiments of theinstant invention, dispersion is compensated numerically by flatteningthe Fourier domain phase of a mirror reflection. Current proposedprocedure comprises of:

-   a) Measuring the interferogram by placing a mirror in the sample,    computing the complex envelope m_(s)(z)=A_(m)(z)Exp(jφ_(m)(z)) [Here    z is distance in depth, A_(m) is amplitude and φ_(m) is phase) for    the interferogram. Such an intrerferogram can also be measured by    removing the sample/specimen in the sample arm.-   b) Computing the complex envelope for each interferogram measurement    for any desired specimen as described in FIG. 12.-   c) Multiplying the complex envelope by Exp(−jφ_(m)(z)) to perform    dispersion compensation.

Coherent Deconvolution or complex deconvolution for DispersionCompensation: Another process known as coherent deconvolution. Thecoherent deconvolution process comprises of

-   a) Measuring the interferogram by placing a mirror in the sample,    computing the complex envelope m_(s)(z)=A_(m)(z)Exp(jφ_(m)(z)) (Here    z is distance in depth, A_(m) is amplitude and φ_(m) is phase) for    the interferogram. S such an intrerferogram can also be measured by    removing the sample/specimen in the sample arm.-   b) Computing the Fourier transform of m_(s)(z) to obtain M_(s)(k),    where k is spatial frequency,-   c) Computing the complex envelope s(z,x) for each interferogram    measurement for any desired specimen,-   d) Computing the Fourier transform of s(z,x) to obtain S(k,x),-   e) Dividing S(k,x) by M_(s)(k) to obtain S₁(k,x),-   f) Multiplying S₁(k,x) by a Wiener filter to obtain S₂(k,x) and-   g) Computing inverse Fourier transform to obtain dispersion    corrected sample measurement s₂(z, x).

In FIG. 13, Doppler processing algorithm for high accuracy and highprecision velocity estimation is described (step 1302). The data setresulting from the camera can be processed in the processor 414 by theproposed Doppler algorithm which computes STFT (short time Fouriertransforms) in lateral (x) direction (step 1306).

$\begin{matrix}{{\hat{S}\left( {z,x,f} \right)} = {\sum\limits_{m = {{- N_{x}}/2}}^{{N_{x}/2} - 1}{{s\left( {z,{\left( {x + m} \right)T}} \right)}{\exp\left\lbrack {{- j}\; 2\;\pi\;{fmT}} \right\rbrack}}}} & \left( {{Eq}\mspace{14mu} 8} \right)\end{matrix}$where N_(x) is the number of A-scans in the STFT window. Next the peakof the STFT spectrum is estimated (step 1308). Next, the Doppler shiftis computed by an adaptive centroid algorithm (which computes centroidusing the power near the peak of the STFT spectrum) (step 1310). Next,the velocity is estimated using Doppler shifts and Velocity images/mapsare generated (step 1312). Step 1314 is the end of Doppler processing.The velocity precision is given byV _(s) ^(up) =c/(2N _(x) Tv ₀ n _(t) cos θ)  (Eq 9)

Doppler shift algorithm is used for estimating Doppler shifts bycomputing the centroid of the short time Fourier transform spectrumusing power near the spectral peak, which is an adaptive centroidalgorithm. As we can see, velocity precision is higher with higher T(A-scan acquisition period). Therefore, in order to detect micro-flow(˜100 to 800 microns/s speed) in capillaries, by way of example but notby limitation, we can choose an A-scan rate of e.g., 2560 A scans/s. Themaximum retinal blood flow velocities typically range to 1-4 cm/s. Byway of example but not by limitation, higher velocities can be measuredby performing another scan at a much higher speed of 42000 A scans/s. Byway of example but not by limitation, from Eq. 4, choosing N_(x) between1 to 30, we can measure velocities as low as 15 mm/s to 0.5 mm/s,respectively. By way of example but not by limitation, we can scanretina at 2 different scan rates, viz., 2560 A scans/s and 42000 Ascans/s. By way of example but not by limitation, in the first set, wecan scan 10 concentric circles centered at the optic disc, eachcomprising of 100 A-scans, which can be acquired in 4 seconds. By way ofexample but not by limitation, the second set would be acquired at thesame locations, 10 concentric circles, each consisting of 420 A-scans,which can be acquired in 1 s. The scanning may be performed by the discof the retina by performing concentric circles at a variety of speed.Optical delivery unit in the sample arm creates scan patterns, whereinthe scan-pattern comprises of at least two B-scans, each B-scan havingits specific A-scan rate.

Thus, we propose scan-patterns comprising of at least two B-scanswherein the first B-scan's A-scan rate is slower than the A-scan rate inthe second B-scan.

In an embodiment, the scan-pattern can comprise of at least two B-scans,each B-scan having its specific A-scan rate.

This Doppler processing step can used to estimate blood flow velocitiesfor augmenting diagnosis of diabetic retinopathy. By acquiring B-scansat various locations, this can be used to obtain a 3-dimensional map ofblood flow velocities or blood vessels in the retina as well as anyorgan of a human or animal body.

The method of FIG. 11 is also applicable for an OFDR-OCT system. In theOFDR-OCT system, the light entering the detector arm from the beamsplitter is incident on the detector and converts to an interferometricelectric current or signal. The tunable light source produces a light ofvarious frequencies within a specific bandwidth. Thisfrequency/wavelength sweeping is performed at a very high speed and thedetector is able to measure the interference signal at each of thefrequencies. Such a high speed measurement produces a spectrum forfurther processing (step 1104 in FIG. 11). These spectra are typicallymeasured at equal intervals of wavelength. Therefore, the spectrameasured by the detector are processed using a re-sampling algorithm.Thus, the spectra are resampled at equal intervals of spatial frequency(k-space) (step 1106). There are some specialized OFDR-OCT systems wherethe source is able to sweep the bandwidth at equal intervals of spatialfrequency (k-space). In those cases, the resampling algorithm is notneeded. Next the signal is demodulated to extract its complex envelope(step 1108) and generate A-scans. The absolute part of the complexenvelope (A-scan) is traditional OFDR-OCT signal. Next, the dispersioncompensation is performed so that the signal has better depth resolutionand higher fidelity (step 1110). Finally, Doppler processing isperformed to obtain velocity images, which has velocity informationwithin various locations within a specimen (or an eye) (step 1112).

Foldable System Description

OCDR-OCT system 400 and OFDR-OCT 600 are able to image sub-surfaceretinal microstructure and has been useful for diagnosis and managementof diabetic retinopathy.

In some other embodiments, the foldable face-holder system is used foroptical coherence tomography (OCT) imaging and the OCT system comprisesof a depth-scanning reference mirror to implement time-domain OCT (asdescribed in Huang et al 1991, Fercher 1996, U.S. Pat. No. 5,321,501).

In some embodiments, compact, portable OCT-OCDR systems/apparatus (asdescribed in U.S. patent application Ser. Nos. 12/706,717, 12/732,484,13/723,006, 12/941,991) can be used as these systems/apparatus caneasily fit in a box or a briefcase.

Various materials can be used to construct the foldable face-holderapparatus/system. Some examples are (not by limitation) 6061 aluminumalloy (i.e., UNS A96061) and its various varieties including (but notlimited to) 6061-O, 6061-T4, 6061-T4 etc.; Nickel-chromium alloys suchas INCONEL® (a registered trademark of the INCO family of companies)alloy 600; stainless steel and related alloys (e.g., UNS N02200, UNSN02201, UNS N04400, UNS N06600, UNS N06625, UNS N08800, UNS N08825, UNSN10276, UNS N08020, etc.) heat and chemical resistant polymers such asTOPAS® COC (by Topas Advanced Polymers). Acetal homopolymer such asDupont's Delrin® can also be used as these polymers are tough, cansustain high stress and strain and are strong, and yet easily moldable.

Some more materials that can be used to construct the foldableface-holder apparatus or system include (not by limitation) High-densitypolyethylene (HDPE), Polyvinyl chloride (PVC), Acrylonitrile butadienestyrene (ABS), Polyether ether ketone (PEEK).

The apparatus or system can be built (by way of example and not bylimitation) by the process of reaction injection molding, which canproduce high-strength, lightweight and flexible parts usingthermosetting polymers such as polyurethane.

The apparatus or system could also be built (by way of example and notby limitation) by structural reaction injection molding (SRIM), wherefiber meshes are used as a reinforcing agent.

The apparatus or system could also be built (by way of example and notby limitation) by injection molding, using thermoplastics orthermosetting plastics.

The apparatus or system could also be built (by way of example and notby limitation) by normal machining and assembly.

In some embodiments, the chin-rest and/or the face-holder can slide inand out from the side of the ophthalmic system's base. In someembodiments the base comprises of OCT/OCDR/OFDR components.

In some embodiments, the chin-rest and/or the face-holder can be foldedcompletely and slides in the instruments' system's side. In someembodiments the base comprises of OCT/OCDR/OFDR components.

In some embodiments, the ophthalmic system comprises of at least onemeans to hold the face of a patient (i.e., face-holder), an oculardiagnostic or therapeutic component and the means to remove theface-holder 112 from the apparatus/system and attach to the patient'sface. The face-holder's eye-piece 112 is attached to the eyes using ahead-band.

In some other embodiments, the face-holder is attached to the eyes usingspectacles-type assembly. The eye-piece may be moved from one eye to theother for analyzing both the eyes. The eye-piece may be a part of theoptical delivery unit focusing light on the eye.

In some embodiments the face-holder comprises of the optical deliveryunit of the sample arm of the OCT/OCDR/OFDR systems describedpreviously.

In some embodiments, the optical delivery unit is integrated with theface-holder of the foldable ophthalmic system.

In some embodiments the eye-piece is a part of the optical delivery unitof the sample arm of the OCT/OCDR/OFDR systems described previously.

In some embodiments the spectacles type assembly facilitates themovement of the optical delivery unit of the sample arm of theOCT/OCDR/OFDR system from one eye to the other for analyzing both theeyes.

In some embodiments, the spectacles type assembly facilitates themovement of the eye-piece of at least one of the fundus photographysystem, scanning retinal imaging system, perimeter, corneal topographer,auto-refractors, and many other ophthalmic modalities from one eye tothe other for analyzing both the eyes.

The foldable face-holder apparatus/system and related systems couldcomprise of fundus photography(http://en.wikipedia.org/wiki/Fundus_photography), scanning retinalimaging (e.g., T R Friberg, A Pandya et al 2003), perimetry, cornealtopography, auto-refractors, and many other ophthalmic modalities.

INDUSTRIAL APPLICATIONS

OCDR-OCT system and apparatus of this instant application is very usefulfor diagnosis and management of ophthalmic diseases such as retinaldiseases and glaucoma etc. Instant innovative OCDR-OCT diagnostic systemleverages advancements in cross technological platforms. This enables usto supply the global market a low-cost, portable, robust OCDR-OCTimaging tool, which would be affordable to general physicians,optometrists and other health personnel.

The ophthalmic system and apparatus of this instant application is veryuseful for diagnosis and management of ophthalmic diseases such asretinal diseases and glaucoma etc. Instant innovative ophthalmicdiagnostic system leverages advancements in cross technologicalplatforms. This enables us to supply the global market a low-cost,portable, robust ophthalmic tool, which would be affordable to generalphysicians, optometrists and other health personnel.

It is to be understood that the embodiments described herein can beimplemented in hardware, software or a combination thereof. For ahardware implementation, the embodiments (or modules thereof) can beimplemented within one or more application specific integrated circuits(ASICs), mixed signal circuits, digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, graphicalprocessing units (GPU), controllers, micro-controllers, microprocessorsand/or other electronic units designed to perform the functionsdescribed herein, or a combination thereof.

For a mechanical hardware implementation, the embodiments (or modulesthereof) can be implemented using various fabrication or prototypingmethods.

When the embodiments (or partial embodiments) are implemented insoftware, firmware, middleware or microcode, program code or codesegments, they can be stored in a machine-readable medium (or acomputer-readable medium), such as a storage component. A code segmentcan represent a procedure, a function, a subprogram, a program, aroutine, a subroutine, a module, a software package, a class, or anycombination of instructions, data structures, or program statements. Acode segment can be coupled to another code segment or a hardwarecircuit by passing and/or receiving information, data, arguments,parameters, or memory contents.

What is claimed is:
 1. An ophthalmic system comprising of at least onemeans to hold the face of a patient called a face-holder; wherein theface-holder can be folded at least once; and the face-holder furthercomprises of a forehead rest, which is a resting pad to rest theforehead; a light source emitting light of a specific bandwidth called afirst light; the light source operates at a center wavelength λ; a beamsplitter to split the first light from a source arm to a reference armand a sample arm; the sample arm further comprising of an opticaldelivery unit; the optical delivery unit is further integrated with theface-holder; the sample arm sends the second path of light to an eyeusing the optical delivery unit and the eye reflects back the secondpath of light as a returning light via the optical delivery unit to thebeam splitter; a reference mirror in the reference arm returning thefirst path light to the beam splitter to join a returning light from theeye; a partial returning light from the beam splitter travels through adetector arm to a grating unit; the grating unit disperses the partialreturning light from the beam splitter and a dispersed light enters thedetector array to produce a light spectrum; and a processor performs adata analysis using a specific algorithm on the light spectrum; and theprocessor generates A-scans of the eye; a base; and the system fits inat least one of a box, a tablet and a briefcase; and the systemcomprises of at least one of ophthalmic imaging, perimetry, cornealtopography, auto-refractors, fundus photography, scanning retinalimaging, and a therapeutic component.
 2. The system of claim 1; furthercomprising of at least one part made using at least one of High-densitypolyethylene, Polyvinyl chloride, Acrylonitrile butadiene styrene,Polyether ether ketone, 6061 aluminum alloy, various varieties of 6061aluminum alloy, Nickel-chromium alloys, stainless steel, stainless steelrelated alloys, heat and chemical resistant polymers, and Acetalhomopolymer.
 3. The system of claim 1; where at least one part of thesystem is built using at least one of machining, structural reactioninjection molding, reaction injection molding, injection molding,thermoplastics and thermosetting plastics.
 4. The system of claim 1;wherein the specific algorithm further comprises of at least one offrequency resampling, demodulation, dispersion compensation, and Dopplerprocessing algorithms.
 5. The system of claim 4; wherein the frequencyresampling comprises of at least one of linear interpolation, splineinterpolation, convolution using a Kaiser-Bessel window; thedemodulation algorithm comprises of a modified Hilbert transform wherethe light spectra are Fourier transformed in a lateral direction; thedispersion compensation comprises of at least one of coherentdeconvolution and flattening the Fourier domain phase of a mirrorreflection; the Doppler processing algorithm comprises at least one ofshort time Fourier transforms, computing a centroid of the short timeFourier transform; an adaptive centroid algorithm.
 6. The system ofclaim 1; further comprising of at least one feature selected from thefollowing group: the face-holder can be ejected from the base; theface-holder can be folded by collapsing multi-stage telescopic legs; theface-holder comprises of a chin-rest and a forehead rest and only theportion between the chin-rest and the base is collapsible using themulti-stage telescopic legs; a folding hinge near the chin-rest; afolding hinge for the face holder near the instrument base; thechin-rest can be removed using a button from the base; the chin-rest isattached to the base; the chin-rest is attached to a pole of theface-holder; the chin-rest can be removed from the pole of theface-holder; a projector to display; at least one of a touch-sensitivedisplay screen, and a display having stereoscopic capabilities; thesystem operates on at least one of batteries and rechargeable batteries;a vehicle charger to charge the batteries by sourcing power from avehicle; at least one waveplate; an eye-fixation target; the opticaldelivery unit comprises of at least one of galvanometer and a MEMSmirror; the processor generates B-scans using A-scans and the opticaldelivery unit generates scan-patterns comprising of at least twoB-scans, each B-scan having its specific A-scan rate; the eye-piece hasrailings to move it forward and backward with respect to the patient'seye; the chin-rest and the face-holder can be folded completely andslides in the system's side.
 7. The system of claim 6; where at leastone waveplate is a (2M+1)λ/m waveplate where M and m are integers. 8.The system of claim 7; where the waveplate is created using an opticalfiber.
 9. An ophthalmic system comprising of at least one means to holdthe face of a patient called a face-holder; a face holder comprising ofa spectacles-type assembly attached to the eyes; and a tunable lightsource; the tunable light source produces a light of various frequencieswithin a specific bandwidth; a beam splitter to split the first lightfrom a source arm to a reference arm and a sample arm; the sample armfurther comprising of an optical delivery unit; the sample arm sends thesecond path of light to an eye using the optical delivery unit and theeye reflects back the second path of light as a returning light via theoptical delivery unit to the beam splitter; a reference mirror in thereference arm returning the first path light to the beam splitter tojoin a returning light from the eye; a partial returning light from thebeam splitter travels through a detector arm to a detector; the detectorfurther directs the signal to an analog to digital converter to generatea digitized signal; and the digitized signal is directed towards aprocessor; and such a measurement produces spectra; the processoranalyzes the digitized signal using a specific algorithm; and theprocessor generates A-scans of the eye; at least one of a projector todisplay and a display screen; a base; and the system fits in at leastone of a box, a tablet and a briefcase.
 10. The system of claim 9;wherein the specific algorithm further comprises of at least one offrequency resampling, demodulation, dispersion compensation, and Dopplerprocessing algorithms.
 11. The system of claim 10; wherein the frequencyresampling comprises of at least one of linear interpolation, splineinterpolation, convolution using a Kaiser-Bessel window; thedemodulation algorithm comprises of a modified Hilbert transform wherespectra are Fourier transformed in a lateral direction; the dispersioncompensation comprises of at least one of coherent deconvolution andflattening the Fourier domain phase of a mirror reflection; the Dopplerprocessing algorithm comprises at least one of short time Fouriertransforms, computing a centroid of the short time Fourier transform; anadaptive centroid algorithm.
 12. The system of claim 9; where theprocessor is selected from a group consisting of a computer, anintegrated circuit, an application specific integrated circuit, a fieldprogrammable gate array, a graphical processing unit, an embedded systemand a microcontroller.
 13. The system of claim 9 further comprising ofat least one feature selected from the following group: an eye-piece inthe spectacles-type assembly may be moved from one eye to the other foranalyzing both the eyes; the face-holder can be ejected from the base;the display screen is at least one of a touch-sensitive screen, and adisplay having stereoscopic capabilities; the system operates on atleast one of batteries and rechargeable batteries; a vehicle charger tocharge the batteries by sourcing power from a vehicle; an eye-fixationtarget; the optical delivery unit comprises of at least one ofgalvanometer and a MEMS mirror.
 14. The system of claim 9, where in atleast one of the tunable light source, the processor, the reference arm,the sample arm, the detection arm, the beam splitter, the detectorreside in the base.
 15. An ophthalmic system comprising of at least onemeans to hold the face of a patient called a face-holder; wherein theface-holder can be folded at least once; and a base; and at least one ofophthalmic imaging, perimetry, corneal topography, auto-refractors,fundus photography, scanning retinal imaging, optical coherencetomography and a therapeutic component; and further comprising of atleast one feature selected from the following: the system fits in atleast one of a box, a tablet and a briefcase; a face holder comprisingof a spectacles-type assembly attached to the eyes; an eye-piece in thespectacles-type assembly may be moved from one eye to the other foranalyzing both the eyes; wherein at least one part of the system isbuilt using at least one of machining, structural reaction injectionmolding, reaction injection molding, injection molding, thermoplasticsand thermosetting plastics.
 16. The system of claim 15; furthercomprising of at least one feature selected from the following group: abase; the face-holder can be ejected from the base; the face-holder canbe folded by collapsing multi-stage telescopic legs; the face-holdercomprises of a chin-rest and a forehead rest and only the portionbetween the chin-rest and the base is collapsible using the multi-stagetelescopic legs; there is a folding hinge near the chin-rest; there is afolding hinge for the face holder near the instrument base; thechin-rest can be removed using a button from the base; the chin-rest isattached to the base; the chin-rest is attached to a pole of theface-holder; the chin-rest can be removed from the pole of theface-holder; an eye-fixation target; the system operates on at least oneof batteries and rechargeable batteries; a vehicle charger to charge thebatteries by sourcing power from a vehicle; a projector to display; atleast one of a touch-sensitive screen and a display having stereoscopiccapabilities; the face-holder further comprises of a forehead rest,which is a resting pad to rest the forehead.
 17. The system of claim 15further comprising of at least one part made using a material selectedfrom a group consisting of High-density polyethylene, Polyvinylchloride, Acrylonitrile butadiene styrene, Polyether ether ketone, 6061aluminum alloy, various varieties of 6061 aluminum alloy,Nickel-chromium alloys, stainless steel, stainless steel related alloys,heat and chemical resistant polymers, and Acetal homopolymer.
 18. Thesystem of claim 15 further comprising of at least one of evaluation andtreatment of an organ selected from a group consisting of a retina, aposterior segment, a cornea, and an anterior segment.